The viscosity of oils of lubricating viscosity is generally dependent upon temperature. As the temperature of the oil is increased, the viscosity usually decreases, and as the temperature is reduced, the viscosity usually increases.
The function of a viscosity improver is to reduce the extent of the decrease in viscosity as the temperature is raised or to reduce the extent of the increase in viscosity as the temperature is lowered, or both. Thus, a viscosity improver ameliorates the change of viscosity of an oil containing it with changes in temperature. The fluidity characteristics of the oil are improved since the oil maintains a more consistent viscosity over a wider range of temperatures.
It is desirable that the viscosity improver not adversely affect the low-temperature viscosity of the lubricant containing same. Frequently, while many viscosity improvers enhance the high temperature viscosity characteristics of lubricating oil, the low temperature properties of the treated lubricant become worse.
Viscosity improvers are usually polymeric materials and are often referred to as viscosity index improvers and sometimes as viscosity modifiers.
Many ethylene derived polymers, especially ethylene-propylene copolymers are known and are used as viscosity improvers for lubricating oils compositions. Ethylene-propylene copolymers with high ethylene levels (e.g., 70-78 weight %) when used as viscosity modifiers in lubricants impart outstanding low temperature properties as measured by Cold Crank Simulator (CCS) ASTM Procedure D−5293 and Mini-Rotary Viscometer (MRV-TP1) ASTM Procedure D−4684. However, it has also been observed that formulations containing these polymers tend to experience gelation in cold temperature storage, filter plugging in cold temperature engine startup and the “Weissenberg effect during CCS measurement where the lubricant climbs up the rotating shaft of the test apparatus, leading to questionable CCS values. These effects are further exacerbated when the polymers are used with base oils containing synthetic stocks such as polyalphaolefin stocks and synthetic ester stocks.
Additives that provide viscosity improving properties are known in the art. Such products are described in numerous publications including Dieter Klamann, “Lubricants and Related Products”, Verlag Chemie Gmbh (1984), pp 185-193; C. V. Smalheer and R. K. Smith “Lubricant Additives”, Lezius-Hiles Co. (1967); M. W. Ranney, “Lubricant Additives”, Noyes Data Corp. (1973), pp 92-145, M. W. Ranney, “Lubricant Additives, Recent Developments”, Noyes Data Corp. (1978), pp 139-164; and M. W. Ranney, “Synthetic Oils and Additives for Lubricants”, Noyes Data Corp. (1980), pp 96-166.
U.S. Pat. No. 3,389,087 discloses amorphous-crystalline polymers comprised of 2-98 weight % ethylene and 2-98 weight % C3-18 alpha olefins having molecular weight ranging from 20,000 to 250,000, a degree of head-to-head linkages ranging between 20% and 60% and a degree of crystallinity up to 25%. Also described are oil compositions containing the polymer.
U.S. Pat. No. 3,551,336 describes polymers comprised of ethylene (60-80 mole %) and C3-18 alpha olefins having viscosity average molecular weight ranging from 10,000 to 200,000, Mw/ Mn less than 4 and a degree of crystallinity less than 25% and containing no more than 1.3% by weight of a polymer fraction which is insoluble in n-decane at 45° C. Also described are oil compositions containing the polymer.
U.S. Pat. No. 3,522,180 describes amorphous ethylene-propylene copolymers containing 20-70 mole % propylene and Mn of 10,000 to 40,000 and Mw/ Mn less than 5 which are said to be useful as viscosity index improvers for lubricating oil.
U.S. Pat. No. 3,691,078 relates to lubricating oil compositions comprising a neutral, non-volatile mineral oil, a pour point depressant and a viscosity improver consisting of an oil-soluble, substantially linear hydrocarbon polymer containing 25-55 weight % polymerized ethylene units and 75-45 weight % polymerized comonomer units. It is stated that the polymers do not adversely affect the pour point depressant.
U.S. Pat. No. 4,540,753 discloses a copolymer of at least 10 weight % up to 90 weight % ethylene and at least one other alpha-olefin monomer which copolymer is intramolecularly heterogeneous and intermolecularly homogeneous, has Mw from 2,000 up to 12,000,000 and Mw/ Mn less than 2 and/or Mz/ Mw less than 1.8. The polymers are described as being useful as viscosity improver for lubricating oils.
U.S. Pat. No. 4,804,794 discloses copolymers of alpha-olefins comprised of intramolecularly heterogeneous and intermolecularly homogeneous copolymer chains. At least one segment of the copolymer, constituting at least 10% of the copolymer's chain, is a crystallizable segment wherein the ethylene content is at least 55 weight % and the low crystallinity segment contains no more that 53 weight % ethylene.
U.S. Pat. No. 4,959,436 is directed to copolymers of ethylene and at least one other alpha olefin monomer which copolymer is intramolecularly heterogeneous and intermolecularly homogeneous, wherein at least two portions of an individual intermolecularly heterogeneous chain, each portion comprising at least 5 weight % of the chain, differ in composition from one another by at least 5 weight % ethylene and has Mw/ Mn less than 2 and/or Mz/ Mw less than 1.8
U.S. Pat. No. 3,697,429 discloses a lubricating oil composition comprising a lubricating oil and contained therein an amount sufficient to modify the viscosity index of said oil, a viscosity index improving amount of an oil-soluble polymer composition comprising a first copolymer of ethylene and a C3-18 alpha-olefin having an ethylene content of 50-95 mole % and a second copolymer of ethylene and a C3-18 alpha-olefin having an ethylene content of 5-80 mole %, the ethylene content of the first copolymer being at least 5 mole % more than the ethylene content of the second copolymer.
U.S. Pat. No. 4,507,515 discloses a lubricating oil composition comprising an ethylene alpha-olefin copolymer having a major and a minor portion, the major portion having Mw of 10,000 to 500,000, a Mooney viscosity at 100° C. of 0.5 to 500, 10-60 weight % ethylene and ethylene sequence distribution such that the mean number of ethylene units in sequence equal to or greater than 3 consecutive ethylene units is a value of 3 to 4.5 and the fraction of ethylene sequences containing three or more ethylene units is 0.01 to 0.3 based on the total number of ethylene sequences in the major portion and the minor portion having Mw of 1,000 to 2,000,000, an ethylene sequence of 55 to 95% ethylene, an ethylene sequence distribution such that the mean number of ethylenes in sequences greater than or equal to three consecutive ethylene units is 4 to 20 and the fraction of ethylene sequences containing three or more consecutive ethylene units is 0.35 to 0.95, based on the total number of ethylene sequences in the minor portion.
U.S. Pat. Nos. 5,391,617; 5,451,636 and 5,451,630 describe a sheared blend and a process for producing the sheared blend and lubricating oils containing the sheared blend in which high ethylene content (65-85 mole %) and low ethylene content (35-65 mole %) ethylene-propylene copolymers, each having Mn 40,000 to 250,000 and Mw/ Mn 2-7 are subjected to simultaneous blending and shearing.
U.S. Pat. Nos. 5,382,630 and 5,382,631 disclose linear interpolymer blends made from components having Mw/ Mn≦3 and composition distribution>50%. The blend components can all have the same molecular weight but different comonomer contents, the same comonomer content but different molecular weights or comonomer contents which increase with molecular weight.
U.S. Pat. No. 4,874,820 discloses ethylene alpha-olefin copolymer compositions comprising a first copolymer having Mw/ Mn less than 2 and/or Mz/ Mw less than 1.8 and a second copolymer having Mw/ Mn greater than or equal to 2.
Each of these publications is hereby expressly incorporated herein by reference.
When the polymers disclosed in these patents are used as viscosity modifiers for lubricating oils, frequently the problems of gelation, filter plugging and Weissenberg effect are encountered, making them unsuitable for use in lubricant applications, especially where the lubricant will encounter low temperatures.
An important object of this invention is to provide compositions that reduce the extent of loss of viscosity at high temperatures while not adversely increasing the low temperature viscosity of lubricating oil compositions.
Another object is to provide novel additive concentrates.
A more specific object is to provide additives directed to improving the viscosity properties of a lubricating composition.
Yet another object is to provide lubricants having improved viscosity properties.
Another object is to provide additive concentrates for lubricants.
Other objects will in part be obvious in view of this disclosure and will in part appear hereinafter.